This invention relates to coating by vapor deposition and more particularly to a vapor deposition coating machine that is capable of coating large objects with metal.
Various processes exist for coating substances, particularly metals, with metal, usually for the purpose of enhancing the appearance of the coated substance or protecting the coated substance from its environment, or both. For example, a chromium finish is applied to steel through electroplating procedures to improve the appearance of the steel and to a lesser measure to inhibit oxidation. Similarly, steel is often coated with zinc so as to provide a protective coating as well as a sacrificial anode. Aluminum shapes and the like when subjected to anodizing treatments are provided with attractive and durable coatings.
Of all the metal coating processes, perhaps ion vapor deposition, which is a vacuum vapor plating process, provides the most secure bond between the metal substrate and the metal coating. Indeed, the bond is characterized by relatively deep diffusion between the molecules of the two metals at the interface between those metals. In short, it is similar to a diffusion bond. The effectiveness of the bond to a large measure derives from the ability to thoroughly clean the substrate as an adjunct of the ion vapor deposition process and to deposit the metal coating in a powerful ion bombardment.
Heretofore coating by ion vapor deposition procedures has been confined to relatively small objects, because the machines for practicing such procedures were incapable of accommodating large objects. This left larger objects for other, less effective coating procedures. U.S. Pat. Nos. 3,750,623 and 3,926,147 illustrate the most efficient apparatus heretofore developed for coating by ion vapor deposition. In each, the workpiece that is to be coated is an extremely small object, such as a machine screw. The apparatus does not have the capability of coating large sheet metal shapes or other large objects such as might be utilized in the airframe of a high performance aircraft.